The present development is a catalyst for use in water gas shift processes. The catalyst comprises iron oxide, copper oxide, zinc oxide and alumina, and optionally, potassium oxide.
The water-gas-shift reaction is a well-known reaction suitable for production of hydrogen. Large volumes of hydrogen gas are needed for a number of important chemical reactions, and since the early 1940's, the water-gas-shift (WGS) reaction has represented an important step in the industrial production of hydrogen. For example, the industrial scale water-gas-shift reaction is used to increase the production of hydrogen for refinery hydro-processes and for use in the production of bulk chemicals such as ammonia, methanol, and alternative hydrocarbon fuels.
Typically, the catalysts used in the industrial scale water-gas-shift reaction include either an iron-chromium (Fe—Cr) metal combination or a copper-zinc (Cu—Zn) metal combination. The Fe—Cr oxide catalyst is typically used in industrial high temperature shift (HTS) converters. The industrial HTS converters—which have reactor inlet temperatures of from about 300° C. to about 380° C.—exclusively use the Fe-based catalysts because of their excellent thermal and physical stability, poison resistance and good selectivity. These attributes are especially beneficial when low steam to CO ratios are used and the formation of hydrocarbons is favored. Typically, the commercial catalysts are supplied in the form of pellets containing 8-12% Cr2O3 and a small amount of copper as an activity and selectivity enhancer. However, because of governmental regulations that pertain to chromium-comprising catalysts, it would be advantageous to have a water gas shift catalyst that demonstrates all the benefits of the prior art Fe—Cr catalyst but which does not require chromium in the composition.
The copper-based catalysts function well in systems where the CO2 partial pressure can affect the catalyst performance, so the copper-based catalysts tend to demonstrate more favorable CO conversion at lower temperatures. However, unsupported metallic copper catalysts or copper supported on Al2O3, SiO2, MgO, pumice or Cr2O3 tend to have relatively short lifespan (six to nine months) and low space velocity operation (400 to 1000 h−1). The addition of ZnO or ZnO—Al2O3 can increase the lifetime of the copper-based catalysts, but the resultant Cu—Zn catalysts generally function in a limited temperature range of from about 200° C. to about 300° C. Further, Cu—Zn catalysts tend to be susceptible to poisoning by sulfur-containing compounds. Thus, merely using a Cu-based catalyst or a Cu—Zn catalyst in water gas shift processes is not a viable commercial option.
Thus, there is a need for a stable chromium-free iron-based water gas shift catalyst that performs as well as or better than the prior art iron-chromium catalysts.